Drain flies and fruit flies can both be a problem in kitchen areas any time of year, but especially during warm months and during harvest time. Both are tiny, light colored, and highly attracted to any organic matter. They nest and lay eggs where there is water and rotting food, making drains a choice location. Drain flies are more active at night, but fruit flies are a nuisance at all times of day.
Small flies can be difficult to control once they find their way inside. Restaurant kitchens can be especially vulnerable, but home kitchens are best kept fly-free by quickly refrigerating ripe fruit and vegetables. Reduce your risk by checking produce before bringing it into your home and taking organic debris out of your home immediately.